Agglutination assays may be used to detect the presence of or measure an amount of an analyte in a sample. Typical applications include testing blood serum for the presence of reactive antibodies to known pathogens or testing blood antigen type for donor compatibility. Analytes present in the sample cause particles (e.g. beads) in the sample to interact with each other to form clumps (also called agglutinate or aggregates). Agglutination assays are typically conducted by adding a sample of interest to a suspension of antibody- or antigen-coated particles deposited on a card, and rocking the card manually for a few minutes to facilitate agglutination (clumping). Specific interaction between the antibody/antigen with substances of interest in the sample causes visible aggregation of the particles which serves as the assay readout.
Therefore, a typical agglutination assay is only able to report whether analyte concentration in a sample is above or below a given threshold value (e.g. there are visible clumps of agglutinate or there are not). Furthermore, manual mixing of assay particles and sample by rocking a card can result in a considerable variability of assay conditions yielding a large uncertainty range in the threshold value. Therefore, agglutination assays are typically performed only for applications where the analyte is either present in large quantities in the sample or otherwise almost entirely absent.